High-stable powder prelithiated silicon-based negative electrode material and preparation method thereof

Abstract

The application discloses a high-stability powder prelithiated silicon-based negative electrode material and a preparation method thereof. The material is mainly composed of prelithiated silicon monoxide, a titanium-doped carbon layer, a hydrophobic titanium metallocene layer and a hydrophilic cyclodextrin layer. The ultrasonic cavitation technology is adopted to uniformly prelithiate to improve the initial efficiency, the hydrophobic titanium metallocene coating is adopted to reduce gas production, and the hydrophilic cyclodextrin coating is adopted to improve the dispersion performance of the slurry. The material synthesized by the above method has high initial efficiency, small crystal grains, low residual alkali, good slurry stability and processing performance, and good cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a highly stable powder pre-lithiated silicon-based anode material and its preparation method. Background Technology

[0002] With the development of electric vehicles and portable electronic devices, the demand for high-energy-density lithium-ion batteries is increasing. Traditional graphite anode materials have a theoretical specific capacity of only 372 mAh / g, which is insufficient to meet market demand. Silicon materials, with their initial specific capacity of 4200 mAh / g, higher lithium intercalation platform, abundant crustal reserves, and environmental friendliness, are gradually attracting widespread attention from researchers.

[0003] However, silicon exhibits a volume expansion of up to 300%. During cycling, this not only causes silicon to separate from the surrounding conductive carbon network, forming "dead silicon," but also leads to silicon delamination from the current collector. Secondly, the significant volume expansion causes the surface SEI film to continuously rebuild and break down, making the SEI film increasingly thick and continuously consuming Li+ ions from the cathode, thus reducing coulombic efficiency. Finally, the large volume expansion leads to silicon material pulverization in the later stages of cycling. These problems ultimately result in a sharp deterioration in cycling performance.

[0004] Due to the aforementioned issues, academia and industry have shifted some attention to silicon suboxide. Compared to nano-silicon, silicon suboxide sacrifices some capacity, but its expansion is relatively small (~100%), and the byproducts generated during charge and discharge, such as lithium oxide, lithium silicate, and lithium metasilicate, can provide a buffering effect, greatly improving the material's cycle performance. However, the material's conductivity is relatively poor, resulting in a low first-cycle efficiency. Lee DJ et al. [Lee DJ, Ryou MH, Lee JN, et al. Nitrogen-doped carbon coating for a high-performance SiO anode in lithium-ion batteries[J]. Electrochemistry Communications, 2013, 34: 98-101.] prepared nitrogen-doped carbon-coated SiO materials through liquid-phase mixing and high-temperature carbonization. This material exhibited relatively good cycle performance, but its first-cycle efficiency was low, and it did not improve the intrinsic electronic conductivity of the material. Jee HoYom et al. [Yom JH, Sun WH, Cho SM, et al. Improvement of irreversible behavior of SiO anodes for lithium ion batteries by a solid-state reaction at high temperature[J]. Journal of PowerSources, 2016, 311: 159-166.] prepared high-efficiency silicon-based anode materials by reacting SiO with lithium metal in a solid state followed by carbon coating. This method improved the initial coulombic efficiency of the material, but the cycle performance was relatively poor. Because lithium metal was used as a reactant, the synthesis conditions were relatively harsh, posing safety risks. Due to the pre-lithiation of SiO, a large amount of lithium carbonate and lithium hydroxide were present on the material surface. Furthermore, during storage (due to the presence of water vapor and carbon dioxide in the air) and during aqueous slurry mixing, the lithium silicate inside the material dissolved, further converting into lithium carbonate and lithium hydroxide. This could lead to gas generation and reaction with the binder during battery slurry mixing, deteriorating the cycle performance of the material. Considering the urgent need for pre-lithiated silicon anode materials in battery cells, these shortcomings need to be addressed. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the existing technology and provide a highly stable powder pre-lithiated silicon-based anode material and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The high-stability powder pre-lithiated silicon-based anode material provided by the present invention uses pre-lithiated silicon suboxide as the core, and sequentially coats its surface with a titanium-doped carbon layer, a hydrophobic titanium-based layer, and an outer hydrophilic cyclodextrin coating layer.

[0008] Furthermore, the titanium-doped carbon layer accounts for 2% to 5% of the material mass, the diacetic titanium layer accounts for 0.5% to 5% of the total material mass, and the cyclodextrin accounts for 0.5% to 3% of the total material mass.

[0009] Furthermore, the titanium diacene layer and the carbon layer are bonded by Ti-C bonds.

[0010] The preparation method of the above-mentioned high-stability powder pre-lithiated silicon-based anode material provided by the present invention includes the following steps:

[0011] S1. Crush and classify the SiO material to control the particle size distribution;

[0012] S2. The material obtained in S1 is placed in a kiln under protective gas for carbon coating, discharged at room temperature and deagglomerated;

[0013] S3. Add a mixed solvent of tetrahydrofuran and toluene to the reaction vessel, introduce an inert gas, then add titanium dicene. After complete dissolution, add an organolithium salt and stir mechanically to allow the reaction to proceed.

[0014] S4. After the reaction in S3 is completed, the solution is transferred to the reaction chamber of the ultrasonic cavitation equipment under an inert gas atmosphere. The deagglomerated silica material from S2 is added, the solid content is controlled, and ultrasonic cavitation treatment is carried out using the ultrasonic cavitation effect.

[0015] S5. Dissolve cyclodextrin in dimethylformamide solvent to obtain cyclodextrin solution; after the reaction in S4 is completed, add the cyclodextrin solution to it for secondary treatment, so that the lithiated silicon suboxide material coated with titanium cadmium enters the inner cavity of cyclodextrin.

[0016] S6. After the secondary treatment in S5 is completed, rotary evaporation is performed to obtain the high-stability powder pre-lithiated silicon-based anode material.

[0017] Silicon suboxide (SiO) is limited in its widespread application in lithium-ion batteries due to its poor conductivity, low initial efficiency, and large expansion. This invention utilizes ultrasonic cavitation to create pores under liquid-phase conditions, along with instantaneous high temperature, high pressure, and shock waves, to simultaneously pre-lithiate bis(lithium) titanium diacene on the surface and inside of SiO. This not only increases the contact area and reactive sites, shortens the reaction path, improves reaction uniformity, and reduces surface residual alkali, ultimately improving the material's initial coulombic efficiency, but also controls the reaction intensity, effectively reducing the grain size of single-crystal silicon in SiO, thereby reducing material expansion and improving cycle stability. Furthermore, the titanium diacene tightly bonds with the carbon layer on the surface of the pre-lithiated SiO powder through Ti-C bonds, and Ti is doped into the carbon; the synergistic effect of these two elements improves the material's conductivity. Furthermore, the highly hydrophobic titanium cadmium in the middle layer effectively isolates water vapor in the air and water contact during the slurry mixing process, preventing the dissolution of lithium silicates inside SiO, reducing gas production, and improving slurry stability. The hydrophilic cyclodextrin on the outermost edge improves the slurry dispersibility during the mixing process and enhances the material's processing performance. Through the above approach, the prepared material exhibits good storage stability, high conductivity, high initial efficiency, stable slurry during mixing, minimal volume expansion, and excellent cycle performance.

[0018] Furthermore, the pre-lithiated silicon suboxide is mainly composed of silicon suboxide, silicon, and lithium metasilicate. In XRD, the half-width at half-maximum (WHM) of silicon at 28.4° is between 0.8 and 2, and the intensity of the lithium metasilicate diffraction peak at 26.3° is between 1500 and 4200 ppm. The intensity ratio of the 26.3° to 28.4° diffraction peaks is between 1.2 and 5. By controlling the WHM of 28.4° and the intensity and ratio of the 26.3° diffraction peak, the grain size of the single-crystal silicon and the pre-lithiation depth in the material are controlled. This ensures that while improving the first-time efficiency during the pre-lithiation process, the material's cycle performance does not deteriorate or even further improves. A smaller WHM of 28.4° results in larger silicon grains, greater material expansion, and poorer cycle performance. A larger WHM of 28.4° does not significantly improve the first-time efficiency, thus requiring control. A larger intensity of the 26.3° diffraction peak and a smaller intensity ratio indicate a deeper pre-lithiation depth, larger silicon grains, material structural damage, and poorer cycle performance. The smaller the intensity of the 26.3° diffraction peak and the larger the intensity ratio, the lower the pre-lithiation amount, the less the first-efficiency improvement, and the pre-lithiation is mainly concentrated on the material surface, resulting in excessively fast grain growth and poor cycle performance.

[0019] Furthermore, in step S1, the SiO particle size distribution is as follows: Dmin ≥ 3 μm, D10 ≥ 5 μm, 8 ≤ D50 ≤ 10 μm, and Dmax ≤ 14 μm. By controlling the SiO particle size distribution, the uniformity of carbon coating on the material surface can be controlled. Otherwise, there will be problems such as excessive coating of small particles and insufficient coating of large particles. In the subsequent pre-lithiation process, the pre-lithiation reaction of insufficiently coated particles will be too violent, resulting in severe exothermic reaction, rapid growth of silicon grains, and excessive volume expansion of the material during charge and discharge, ultimately deteriorating the cycle performance of the material.

[0020] Furthermore, in step S2, the protective gas is one or more of nitrogen, helium, neon, argon, etc.; the carbon coating method is gas-phase carbon coating, and the carbon source gas used is one or more of methane and its homologues, ethylene and its homologues, acetylene and its homologues, etc.; the volume ratio of the protective gas to the carbon source gas is 1:1 to 4:1; the carbon coating treatment temperature is 600℃ to 800℃, and the treatment time is 1h to 6h; the kiln rotation speed is 0.25r / min to 2r / min; the deagglomeration can be carried out by mechanical pulverization; the particle size of the deagglomerated material is Dmin≥3μm, D10≥5.5μm, 8.5≤D50≤10.5μm, and Dmax≤15μm. This step primarily aims to coat the material surface with a uniform, dense, and complete carbon layer. This prevents direct contact with active lithium during pre-lithiation, effectively reducing reaction intensity and heat release, and further controlling the growth rate of silicon grains within the material. The coating temperature is chosen to be between 600℃ and 800℃ to maintain the amorphous properties of the SiO material, which is beneficial for controlling silicon grain growth in the subsequent pre-lithiation reaction. If the temperature is too low, the utilization rate of carbon-containing gas will be too low, resulting in more defects in the carbon layer and poor conductivity, affecting not only the material's first-efficiency but also its impedance. If the temperature is too high, SiO will begin a disproportionation reaction, generating silicon nuclei that will grow rapidly during the subsequent pre-lithiation process, deteriorating the material's cycle performance. Since coating can cause material agglomeration, controlling the particle size (the particle size of the carbon-coated SiO after deagglomeration) effectively ensures the integrity of the surface carbon layer coating and further guarantees particle size uniformity, which is beneficial for controlling the pre-lithiation uniformity in the subsequent pre-lithiation process. Otherwise, if the particle size is too large or too small, problems of insufficient or excessive pre-lithiation will occur, ultimately affecting the material's cycle performance.

[0021] Furthermore, in step S3, the inert gas is one or more of helium, neon, argon, etc.; the volume ratio of the tetrahydrofuran and toluene is 1:1 to 2:1; the organolithium salt can be n-butyllithium; the mass ratio of the diacene and the organolithium salt (such as n-butyllithium) is 1:3 to 1:6; the reaction time is 0.5 h to 6 h, and the reaction temperature is 20 °C to 60 °C. The mixed solution of tetrahydrofuran and toluene is mainly used to dissolve the diacene. Because diacene contains delocalized large π bonds, it can react with n-butyllithium. By controlling the reaction temperature and time, monolithium diacene and dilithium diacene can be rapidly generated, and further formed with tetrahydrofuran and lithium to form larger group materials, further increasing the lithium loading. Its potential in the tetrahydrofuran mixed solution is lower than the SiO lithium intercalation potential, serving as a pre-lithiation agent to spontaneously and uniformly pre-lithiate silicon suboxide under liquid phase conditions through potential-driven processes.

[0022] Furthermore, in step S4, the mass ratio of deagglomerated silicon suboxide to lithium in the organolithium salt (such as n-butyllithium) is 9:1 to 19:1; the solid content of the deagglomerated silicon suboxide is 5% to 30%. This step mainly involves using a potential-driven pre-lithiation agent to spontaneously and uniformly pre-lithiate silicon suboxide under liquid phase conditions. Controlling the solid content of silicon suboxide is crucial; too low or too high a solid content leads to severe silicon reduction on the material surface and larger silicon grains, resulting in significant volume expansion and decreased cycle performance. Since the pre-lithiation reaction is potential-driven and relatively slow, the reaction process needs to be controlled. Controlling the mass ratio of silicon suboxide to n-butyllithium improves the material's initial efficiency. A low mass ratio results in only a small improvement in initial efficiency; a high mass ratio, while improving initial efficiency, leads to rapid silicon grain growth, causing significant structural damage and higher surface alkali residue, resulting in a significant decrease in cycle performance.

[0023] Furthermore, in step S4, the ultrasonic power of the ultrasonic cavitation treatment is 50–80 kW, and the ultrasonic intensity is 30–80 W / cm². 2The ultrasonic cavitation treatment lasts for 2 to 8 hours. Preferably, the ultrasonic cavitation treatment is carried out in a cavitator equipped with a sealed reaction chamber, and the operating frequency of the cavitator is 30 to 1000 kHz / s. Since the potential-driven pre-lithiation reaction is slow and has a long time cycle, combining it with ultrasonic cavitation technology can effectively improve reaction uniformity, reduce material grain size, and improve the material's first-efficiency and cycle performance. Specifically, it can further accelerate the fusion of the pre-lithiating agent and silicon suboxide, increase the contact area between the pre-lithiating agent and silicon suboxide, and improve its reactivity. Secondly, after the material is subjected to cavitation impact, cavitation pores will appear inside the silicon suboxide material, allowing the pre-lithiating agent to fully penetrate into the silicon suboxide, thereby increasing the penetration depth. This not only makes the pre-lithiating agent more uniformly dispersed and the reaction path shorter, but also overcomes the problems of reaction dead zones and uneven reaction. Thirdly, the instantaneous high temperature, high pressure, and strong shock wave generated by cavitation cause the pre-lithiating agent to react with the silicon suboxide... The reaction in silicon suboxide not only allows lithium to be uniformly incorporated into the silicon suboxide, improving initial efficiency, but also allows titanium in titanium diaceticum to be doped into the carbon layer on the silicon suboxide surface, improving the conductivity of the carbon material. Furthermore, titanium diaceticum and the carbon layer on the silicon suboxide surface are tightly bonded together through Ti-C bonds. Pre-lithiated silicon suboxide is sensitive to water, while titanium diaceticum is highly hydrophobic, preventing contact with water vapor in the air during material storage and preventing water infiltration during slurry preparation, which could lead to the dissolution of lithium silicates, further improving the stability of the slurry. Compared to traditional solid-state sintering reactions, or even gas-phase reactions (where the reaction is concentrated on the surface and diffuses from the surface to the interior), ultrasonic cavitation can occur simultaneously on the surface and inside, resulting in a shorter and more uniform reaction path and lower residual alkali. Therefore, while improving initial efficiency, it also results in smaller and more uniformly distributed silicon grains, a more stable slurry, and better processing and cycling performance of the material.

[0024] Furthermore, in step S5, the cyclodextrin accounts for 20% to 50% of the total mass of cyclodextrin and dimethylformamide; the mass ratio of the cyclodextrin to the diacene added in step S3 is 1:1 to 1:2; the cyclodextrin can be selected from at least one of the following: α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin; the treatment temperature is 120℃ to 200℃, and the treatment time is 0.5h to 4h. This step mainly involves controlling the temperature / time to immerse the diacene-coated silica material into the inner cavity of the cyclodextrin. Because diacene is hydrophobic, although it can improve the storage stability of the material, it cannot be slurried in an aqueous system. In contrast, the inner cavity of the cyclodextrin is hydrophobic, while the outer surface is hydrophilic. By treating it to introduce the diacene-coated silica material into the inner cavity of the cyclodextrin, not only can the storage stability of the material be improved, but it can also be slurried normally in an aqueous system, effectively preventing the dissolution of lithium silicates, reducing the risk of gas generation during slurry formation, and improving the cycling stability of the material. By controlling the ratio of cyclodextrin to titanium dioxide, the specific charging capacity of the material can be maximized while ensuring material stability. However, an excessively high cyclodextrin ratio leads to decreased conductivity, thus requiring strict control.

[0025] Furthermore, in step S6, the rotary evaporation temperature is 150℃~250℃, and the treatment time is 1h~3h; the obtained pre-lithiated silicon-based anode material has a surface residual lithium ≤200ppm and a pH ≤9. The rotary evaporation method used in this step is mainly to further reduce the residual alkali on the material surface. Through rotary evaporation, the organic solvent evaporates while carrying away some lithium carbonate and lithium hydroxide byproducts from the material surface, lowering the material pH and reducing the risk of gas generation during the slurry mixing process.

[0026] The highly stable powder pre-lithiated silicon-based anode material prepared by the above method also falls within the scope of protection of this invention.

[0027] Another object of the present invention is to provide the application of the above-mentioned highly stable powder pre-lithiated silicon-based anode material in the preparation of lithium-ion batteries. When the silicon-based material of the present invention is used as the anode material to prepare lithium-ion batteries, electrochemical performance tests are performed on the prepared lithium-ion batteries, and the specific capacity, initial efficiency, and cycle stability of the prepared lithium-ion batteries are all improved.

[0028] Traditional silicon suboxide materials suffer from low initial coulombic efficiency. Partially lithiated silicon suboxide, due to the formation of byproducts such as lithium metasilicate, not only exhibits poor pre-lithiation uniformity and large grain size, affecting cycle performance and causing significant volume expansion, but also suffers from high residual alkali on the surface, leading to gas generation in the slurry, poor slurry stability, and reduced adhesion due to side reactions with the binder. This invention aims to improve upon these shortcomings.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] In this invention, pre-lithiation of SiO by using bis-lithium titanium dioxide via liquid-phase reaction not only results in a more uniform reaction and improves the first-efficiency coulombic efficiency of the material, but also allows for control of the reaction intensity, enabling it to proceed under relatively mild conditions. This effectively reduces the grain size of single-crystal silicon in SiO, thereby reducing material expansion and improving the material's cycle stability.

[0031] Under the action of ultrasonic cavitation technology, the titanium element of lithium-loaded titanium-based silicon dioxide is doped into the carbon layer on the SiO surface, improving the electronic conductivity of the material. Furthermore, titanium-based silicon dioxide can tightly bond with the SiO surface through Ti-C bonds. Due to its good electronic conductivity, titanium-based silicon dioxide works synergistically with the carbon layer to reduce material polarization, further improving electronic conductivity. In addition, after being subjected to cavitation impact, cavitation pores appear inside the silicon suboxide material, allowing the pre-lithiating agent to fully penetrate into the silicon suboxide interior, increasing the contact area between the pre-lithiating agent and silicon suboxide, and shortening the reaction path (compared to solid-state sintering). The instantaneous high temperature, high pressure, and strong shock wave generated by cavitation allow the pre-lithiating agent and silicon suboxide to react simultaneously on the surface and inside, resulting in a shorter and more uniform reaction path and lower residual alkali. Therefore, while improving initial efficiency, the silicon grains are smaller and more uniformly distributed, the slurry is more stable, and the material's processing performance and cycle performance are better.

[0032] The core of the material prepared in this invention is pre-lithiated SiO powder, with an inner layer of titanium-doped carbon, a middle layer of highly hydrophobic titanium, and an outer layer of hydrophilic cyclodextrin. The highly hydrophobic titanium coating of SiO extends into the inner cavity of the cyclodextrin (the outer edge of the cyclodextrin is hydrophilic, while the inner cavity is hydrophobic), effectively isolating it from water vapor in the air and water contact during the slurry mixing process, thus preventing the dissolution of lithium silicates. This not only improves the material's storage stability but also prevents gas generation during slurry mixing and enhances the stability of the slurry. The hydrophilic cyclodextrin coating on the outermost layer of the material improves its dispersion performance during the water-washing slurry mixing process.

[0033] Rotary evaporation effectively reduces residual alkali and lithium on the material surface, which can reduce the risk of gas generation during the cell manufacturing process, reduce side reactions between residual alkali and binder, improve bonding performance, and enhance cycle stability.

[0034] This invention employs processes such as crushing, coating, and liquid-phase reaction, resulting in a relatively simple process that is easy to scale up and industrialize. Because it avoids a sintering process, energy consumption is lower, and the silicon grains are smaller and more uniformly distributed.

[0035] The silicon-based anode material prepared by this invention overcomes the shortcomings of traditional SiO materials, improves the initial coulombic efficiency, cycle stability, storage stability and the stability of the material during the cell manufacturing process, while reducing the volume expansion of the material. Attached Figure Description

[0036] Figure 1 SEM image of the silicon-based anode material prepared in Example 1;

[0037] Figure 2 SEM image of the silicon anode material for commercial pre-lithiation in Comparative Example 1;

[0038] Figure 3 SEM image of the silicon-based anode material prepared in Comparative Example 5;

[0039] Figure 4 XRD patterns of the material prepared in Example 1 and the commercially available pre-lithium SiO material in Comparative Example 1;

[0040] Figure 5 The first charge-discharge curve of Example 1 at a current density of 0.1C is shown.

[0041] Figure 6 The cycling performance curves of the full cells of Example 1 and Comparative Example 1 at 1C / 1C current densities are shown. Detailed Implementation

[0042] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0043] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0044] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods.

[0045] Example 1

[0046] SiO materials are subjected to airflow milling and classification to control particle size D. min The diameter of the silicon suboxide (D50) is 3 μm, D10 is 5.2 μm, D50 is 8 μm, and Dmax is 12.4 μm. Then, 3 kg of SiO was placed in a nitrogen-protected rotary kiln, the kiln speed was controlled at 0.25 r / min, the temperature was raised to 750℃, and a mixture of nitrogen and acetylene gas was introduced at a volume ratio of 2:1. The mixture was kept at this temperature for 2 hours, and then discharged at room temperature. After mechanical crushing, the D50 was 8.5 μm, which was denoted as A (i.e., deagglomerated silicon suboxide material).

[0047] Add 500 mL of tetrahydrofuran and 500 mL of toluene to a three-necked flask, mix well, then add 10 g of titanium dicene, stir under an argon atmosphere until completely dissolved, then add 30 g of n-butyllithium, and mechanically stir at 20 °C for 6 h to react.

[0048] The above solution was transferred to the reaction chamber of an ultrasonic cavitation device under argon gas protection. 270g of material A was added. The operating frequency of the ultrasonic cavitation device was controlled at 1000kHz / s, the ultrasonic power at 80KW, and the sound intensity at 80W / cm². 2 Cavitation reaction for 2 hours.

[0049] 10g of cyclodextrin was dissolved in 40g of dimethylformamide solvent. After the ultrasonic cavitation reaction was completed, the cyclodextrin solution was added, and the mixture was stirred at 150℃ for 0.5h. Subsequently, the mixture was transferred to a rotary evaporator for rotary evaporation and treated at 150℃ for 3h under a nitrogen atmosphere to obtain a highly stable powder pre-lithiated silicon-based anode material.

[0050] Figure 1 The SEM image of the silicon-based anode material prepared in Example 1 shows that the particle size is relatively uniform, with particles of about 9 μm, and the material surface is relatively smooth.

[0051] The prepared silicon-based anode material SP:LA133 was mixed and coated in a mass ratio of 8:1:1 to assemble CR2016 coin cells. The electrolyte was a 1 mol / L LiPF6 EC+EMC+DMC solution (volume ratio 1:1:1), and the electrochemical performance was tested.

[0052] The results are as follows Figure 5 As shown in Table 1, at a current density of 0.1C, the material prepared in Example 1 has an initial charge specific capacity of 1414.9 mAh / g, an initial coulombic efficiency of 91.2%, a grain size of 2.4 nm, a residual alkali of 123 ppm, and a pH of 8.7. After 50 cycles, the specific capacity is 1322.5 mAh / g, with a capacity retention of 93.5%.

[0053] Comparative Example 1

[0054] Commercially available pre-lithiated silicon suboxide material is used. The preparation method involves coating silicon suboxide with carbon and mixing it with a lithium source solid phase, followed by high-temperature calcination in a kiln, and then coating the surface with a carbon layer to improve the stability of the material in the slurry.

[0055] Figure 2 The SEM image of Comparative Example 1 shows a large number of dot-like particles on the material surface. This is due to insufficient surface washing, resulting in a large amount of lithium carbonate and lithium hydroxide on the material surface. This leads to high residual alkali and pH on the material surface. The residual alkali will react with the thickener CMC and binder during the slurry mixing process, reducing the bonding performance. This not only affects the process stability of the material in the battery cell, but also reduces the cycle stability of the material.

[0056] Figure 4The XRD patterns of Example 1 and Comparative Example 1 are shown. A comparison reveals that the material prepared in Example 1 exhibits characteristic diffraction peaks of lithium metasilicate (Li₂SiO₃) while the characteristic peaks of crystalline silicon are weaker. This indicates that during the synthesis process, lithium ions react with some silicon / oxygen elements in silicon suboxide, thus reducing the consumption of lithium ions at the cathode during subsequent battery cycles, thereby improving the initial coulombic efficiency of both the material and the battery. Simultaneously, the weaker crystalline silicon peaks and smaller silicon grain size further reduce material expansion. Since lithium metasilicate has a higher elastic modulus than silicon dioxide, it exhibits stronger resistance to volume expansion and superior cycle stability.

[0057] The materials prepared in Example 1 and Comparative Example 1 were respectively mixed with graphite to a concentration of 420 mAh / g as the negative electrode, and NCM811 was used as the positive electrode. A 7Ah soft-pack battery was assembled using processes including slurry preparation, coating, rolling, slitting, die-cutting, stacking, tab welding, top-side sealing, baking, and electrolyte injection. After capacity testing, room temperature cycling tests were conducted at 1C / 1C current density. The results are as follows: Figure 6 As shown. In Example 1, after 400 full-cell cycles, the capacity retention rate was 97%. In Comparative Example 1, after 400 full-cell cycles, the capacity retention rate was 95%. Figure 6 Comparing Example 1 with Comparative Example 1, it can be seen that the material's 400-cycle performance in a full cell is improved by ~2%. This is due to the ultrasonic cavitation technology used in this invention, which results in good pre-lithiation uniformity, smaller grain size, and better structural stability of the synthesized material. Simultaneously, the surface is coated with a double layer of titanium diacene and cyclodextrin, resulting in lower residual alkali, better slurry stability, and better processing performance, thus contributing to better cycle performance. Furthermore, titanium doping with carbon can effectively improve the material's conductivity, reduce polarization, and improve rate performance.

[0058] Comparative Example 2

[0059] Basically the same as Example 1, except that n-butyllithium is not added;

[0060] Comparative Example 3

[0061] Basically the same as Example 1, except that: no titanium dicene is added;

[0062] Comparative Example 4

[0063] Basically the same as Example 1, except that cyclodextrin is not added;

[0064] Comparative Example 5

[0065] The process is basically the same as in Example 1, except that the ultrasonic cavitation technology in Example 1 is not used. Instead, the solution is allowed to stand and settle. After solid-liquid separation, the solid is transferred to an argon atmosphere furnace and sintered at 670°C for 6 hours.

[0066] Figure 3As shown in the SEM image of Comparative Example 5, it can be seen that some materials have a lot of dot-like particles or even hollow states on their surface. This is because ultrasonic cavitation technology was not used, the pre-lithiation reaction was uneven, and the high-temperature heat treatment further accelerated the generation of silicon grains, resulting in an almost hollow state on the material surface and relatively poor cycle performance.

[0067] The materials from Comparative Examples 1-5, SP:LA133, were mixed and coated in a mass ratio of 8:1:1 to assemble CR2016 coin cells. A 1 mol / L LiPF6 EC+EMC+DMC solution (volume ratio 1:1:1) was used as the electrolyte, and electrochemical performance was tested. The results are shown in Table 1.

[0068] Table 1

[0069]

[0070] At a current density of 0.1C, the material prepared in Comparative Example 1 exhibited an initial charge specific capacity of 1372.2 mAh / g, an initial coulombic efficiency of 89.2%, a grain size of 5.4 nm, residual alkali of 350 ppm, and a pH of 11.2. After 50 cycles, the specific capacity was 1213 mAh / g, with a capacity retention of 88.4%. A comparison between Example 1 and Comparative Example 1 reveals that the material prepared in this invention outperforms commercially available materials in terms of specific capacity, initial efficiency, and cycle capacity retention. Furthermore, it exhibits lower residual alkali and pH, less gas generation in water over 24 hours, and smaller grain size. This is because the present invention utilizes ultrasonic cavitation technology for pre-lithiation of the SiO material, resulting in a more uniform reaction. Compared to traditional high-temperature treatment, this method effectively controls the reaction intensity, reduces the grain size of single-crystal silicon in SiO, thereby reducing material expansion and improving cycle performance. Secondly, the hydrophobic-hydrophilic mixed coating on the material surface effectively reduces surface residual alkali and improves slurry stability. The internal hydrophobicity prevents water from penetrating into the material during slurry mixing, preventing internal lithium ion dissolution and reducing gas generation. The hydrophilic nature of the outer edge can improve the dispersion of materials during the mixing process and enhance processing performance.

[0071] By comparing Example 1 with Comparative Example 2, it can be found that the material of the present invention has advantages in first-time efficiency and cycle life, but its capacity is low and its grain size is large. This is because although pre-lithiation can improve the first-time efficiency and improve the shortcomings of insufficient first-time efficiency of SiO, the pre-lithiation process will cause the material grain size to increase due to the high activity of the lithium source, and the non-active lithium silicate formed will cause the material's specific capacity to decrease.

[0072] A comparison of Example 1 and Comparative Example 3 reveals that Example 1 exhibits less gas production, lower residual alkali and pH, and better processing performance. This is because the addition of hydrophobic titanium diaceticate to Example 1 not only reduces residual alkali but also effectively prevents water erosion and lithium ion dissolution from within the material, thereby improving processing and cycle performance. Furthermore, the reduction in residual alkali prevents reaction between residual alkali and the binder, improving electrode adhesion and cycle performance.

[0073] By comparing Example 1 with Comparative Example 4, it can be found that Example 1 has better dispersibility in the slurry mixing process. This is because Example 1 has a layer of hydrophilic cyclodextrin coated on the surface of the titanium dicene. Since cyclodextrin is hydrophilic, it can improve the dispersion of the material in the slurry, thereby improving the circulation.

[0074] A comparison of Example 1 and Comparative Example 5 reveals that Example 1 exhibits smaller grain size, lower residual alkali and pH, and better cycle performance. This is because Example 1 utilizes ultrasonic cavitation technology, which leverages the instantaneous high temperature, high pressure, and strong shock waves generated by cavitation to simultaneously react the pre-lithiating agent with silicon suboxide on the surface and inside. This results in a shorter and more uniform reaction path, lower residual alkali, and thus improved initial efficiency. Furthermore, it produces smaller and more uniformly distributed silicon grains, a more stable slurry, and better processing and cycle performance. Compared to traditional high / low temperature treatments, ultrasonic cavitation offers controllable reaction intensity and better uniformity.

[0075] Based on the above, the material prepared in Example 1 through the above steps and the raw materials and proportions used has better performance.

[0076] Example 2

[0077] SiO material was subjected to airflow milling and classification to control particle sizes Dmin to 3.5 μm, D10 to 6 μm, D50 to 9 μm, and Dmax to 13 μm. Then, 3 kg of SiO was placed in a nitrogen-protected rotary kiln, with the kiln speed controlled at 2 r / min and the temperature raised to 800℃. A mixture of nitrogen and acetylene gas was introduced at a volume ratio of 4:1 and kept at this temperature for 1 hour. The material was then discharged at room temperature. After mechanical milling, the D50 was 9.5 μm, which was denoted as A.

[0078] Add 1000 mL of tetrahydrofuran and 1000 mL of toluene to a three-necked flask, mix well, then add 10 g of titanium dicene, stir under a helium atmosphere until completely dissolved, then add 30 g of n-butyllithium, and mechanically stir at 60 °C for 2 h to react.

[0079] The above solution was transferred to the reaction chamber of an ultrasonic cavitation device under argon gas protection. 570g of material A was added. The operating frequency of the ultrasonic cavitation device was controlled at 1000kHz / s, the ultrasonic power at 70KW, and the sound intensity at 50W / cm². 2 Cavitation reaction for 4 hours.

[0080] 5g of cyclodextrin was dissolved in 20g of dimethylformamide solvent. After the ultrasonic cavitation reaction was completed, the cyclodextrin solution was added, and the mixture was stirred at 200°C for 0.5h. Subsequently, the mixture was transferred to a rotary evaporator for rotary evaporation and treated at 250°C for 3h under a nitrogen atmosphere to obtain the product of this invention.

[0081] The prepared silicon-based anode material (SP:LA133) in a ratio of 8:1:1 was slurried, coated, and used to assemble CR2016 coin cells. A 1 mol / L LiPF6 EC + DMC solution was used as the electrolyte, and electrochemical performance was tested. The test results are shown in Table 2. The material prepared in Example 2 had a grain size of 1.6 nm, residual alkali of 152 ppm, pH of 8.8, an initial charge specific capacity of 1450.2 mAh / g, and an initial coulombic efficiency of 87.2%. The slurry was in normal condition; after 72 hours of resting, 0.2 mg of gas was generated; and after 50 cycles at 0.1C, the capacity retention was 95.4%.

[0082] Example 3

[0083] SiO material was subjected to airflow milling and classification to control the particle size Dmin to 3.5 μm, D10 to 6 μm, D50 to 9 μm, and Dmax to 13 μm. Then, 3 kg of SiO was placed in a nitrogen-protected rotary kiln, the kiln speed was controlled at 2 r / min, the temperature was raised to 600℃, and a mixture of nitrogen and acetylene gas was introduced at a volume ratio of 1:1. The mixture was kept at this temperature for 6 h, and then discharged at room temperature. After mechanical milling, the D50 was 9.5 μm, which was denoted as A.

[0084] Add 1000 mL of tetrahydrofuran and 500 mL of toluene to a three-necked flask, mix well, then add 5 g of titanium dicene, stir under a helium atmosphere until completely dissolved, then add 30 g of n-butyllithium, and mechanically stir at 40 °C for 4 h to react.

[0085] The above solution was transferred to the reaction chamber of an ultrasonic cavitation device under argon gas protection. 270g of material A was added, and the operating frequency of the ultrasonic cavitation device was controlled at 500kHz / s, the ultrasonic power at 50KW, and the sound intensity at 30W / cm². 2 Cavitation reaction for 8 hours.

[0086] 5g of cyclodextrin was dissolved in 20g of dimethylformamide solvent. After the ultrasonic cavitation reaction was completed, the cyclodextrin solution was added, and the mixture was stirred at 200°C for 0.5h. Subsequently, the mixture was transferred to a rotary evaporator for rotary evaporation and treated at 250°C for 3h under a nitrogen atmosphere to obtain the product of this invention.

[0087] The prepared silicon-based anode material (SP:LA133) in a ratio of 8:1:1 was slurried, coated, and used to assemble CR2016 coin cells. A 1 mol / L LiPF6 EC+DMC solution was used as the electrolyte, and electrochemical performance was tested. The nano-silicon material was also tested using the same steps. The results are shown in Table 2. The material prepared in Example 3 had a grain size of 2.8 nm, residual alkali of 184 ppm, a pH of 9.1, an initial charge specific capacity of 1406.7 mAh / g, and an initial coulombic efficiency of 90.6%. The slurry was in normal condition; after 72 hours of resting, 0.4 mg of gas was generated; and after 50 cycles at 0.1C, the capacity retention was 92.7%.

[0088] Example 4

[0089] SiO material was subjected to airflow milling and classification to control particle sizes Dmin to 4 μm, D10 to 6 μm, D50 to 10 μm, and Dmax to 12 μm. Then, 3 kg of SiO was placed in a nitrogen-protected rotary kiln, with the kiln speed controlled at 1 r / min and the temperature raised to 700℃. A mixture of nitrogen and acetylene gas was introduced at a volume ratio of 1:1 and kept at this temperature for 3 h. The material was then discharged at room temperature. After mechanical milling, the D50 was 10.5 μm, which was denoted as A.

[0090] Add 500 mL of tetrahydrofuran and 500 mL of toluene to a three-necked flask, mix well, then add 5 g of titanium dicene, stir under a helium atmosphere until completely dissolved, then add 20 g of n-butyllithium, and mechanically stir at 60 °C for 0.5 h to react.

[0091] The above solution was transferred to the reaction chamber of an ultrasonic cavitation device under argon gas protection. 230g of material A was added. The operating frequency of the ultrasonic cavitation device was controlled at 100kHz / s, the ultrasonic power at 70KW, and the sound intensity at 60W / cm². 2 Cavitation reaction for 8 hours.

[0092] 5g of cyclodextrin was dissolved in 20g of dimethylformamide solvent. After the ultrasonic cavitation reaction was completed, the cyclodextrin solution was added, and the mixture was stirred at 180°C for 2 hours. Subsequently, the mixture was transferred to a rotary evaporator for rotary evaporation and treated at 200°C for 2 hours under a nitrogen atmosphere to obtain the product of this invention.

[0093] The prepared silicon-based anode material (SP:LA133) in a ratio of 8:1:1 was slurried, coated, and used to assemble CR2016 coin cells. A 1 mol / L LiPF6 EC + DMC solution was used as the electrolyte, and electrochemical performance was tested. The test results are shown in Table 2. The material prepared in Example 4 had a grain size of 2.2 nm, residual alkali of 168 ppm, a pH of 8.9, an initial charge specific capacity of 1397.4 mAh / g, and an initial coulombic efficiency of 89.7%. The slurry was in normal condition; after 72 hours of resting, 0.8 mg of gas was generated; and after 50 cycles at 0.1C, the capacity retention was 94.6%.

[0094] Example 5

[0095] SiO material was subjected to airflow milling and classification to control the particle size Dmin to 3.5 μm, D10 to 6 μm, D50 to 9 μm, and Dmax to 13 μm. Then, 3 kg of SiO was placed in a nitrogen-protected rotary kiln, the kiln speed was controlled at 2 r / min, the temperature was raised to 600℃, and a mixture of nitrogen and acetylene gas was introduced in a 1:1 ratio. The mixture was kept at this temperature for 6 h, and then discharged at room temperature. After mechanical milling, the D50 was 9.5 μm, which was denoted as A.

[0096] Add 1000 mL of tetrahydrofuran and 500 mL of toluene to a three-necked flask, mix well, then add 5 g of titanium dicene, stir under a helium atmosphere until completely dissolved, then add 30 g of lithium metal, and stir mechanically at 40 °C for 4 h to react.

[0097] The above solution was transferred to the reaction chamber of an ultrasonic cavitation device under argon gas protection. 270g of material A was added, and the operating frequency of the ultrasonic cavitation device was controlled at 10kHz / s, the ultrasonic power at 80KW, and the sound intensity at 80W / cm². 2 Cavitation reaction for 6 hours.

[0098] 2.5 g of cyclodextrin was dissolved in 12.5 g of dimethylformamide solvent. After the ultrasonic cavitation reaction was completed, the cyclodextrin solution was added, and the mixture was stirred at 160 °C for 1 h. Subsequently, the mixture was transferred to a rotary evaporator for rotary evaporation and treated at 200 °C for 1 h under a nitrogen atmosphere to obtain the product of the invention.

[0099] The prepared silicon-based anode material (SP:LA133) in a ratio of 8:1:1 was slurried, coated, and used to assemble CR2016 coin cells. A 1 mol / L LiPF6 EC+DMC solution was used as the electrolyte, and electrochemical performance was tested. The nano-silicon material was also tested using the same steps. The results are shown in Table 2. The material prepared in Example 5 had a grain size of 3.4 nm, residual alkali of 264 ppm, a pH of 9.5, an initial charge specific capacity of 1389.6 mAh / g, and an initial coulombic efficiency of 91.7%. The slurry was in normal condition; after 72 hours of resting, 1.2 mg of gas was generated; and after 50 cycles at 0.1C, the capacity retention was 91.3%.

[0100] Table 2

[0101]

Claims

1. A pre-lithiated silicon-based anode material, comprising a pre-lithiated silicon suboxide core, on which a titanium-doped carbon layer, a hydrophobic titanium-based layer, and an outer hydrophilic cyclodextrin coating layer are sequentially coated.

2. The pre-lithiated silicon-based anode material according to claim 1, characterized in that: The carbon layer accounts for 2% to 5% of the material mass, the titanium diacene accounts for 0.5% to 5% of the total material mass, and the cyclodextrin accounts for 0.5% to 3% of the total material mass.

3. The pre-lithiated silicon-based anode material according to claim 1 or 2, characterized in that: The pre-lithiated silicon suboxide is mainly composed of silicon suboxide, silicon and lithium metasilicate. Alternatively, the diacene layer and the titanium-doped carbon layer are bonded by Ti-C bonds.

4. A method for preparing the pre-lithiated silicon-based anode material according to any one of claims 1-3, comprising the following steps: S1. Crush and classify the SiO material to control the particle size distribution; S2. The material obtained in S1 is placed in a kiln under protective gas for carbon coating, discharged at room temperature and deagglomerated; S3. Add a mixed solvent of tetrahydrofuran and toluene to the reaction vessel, introduce an inert gas, then add titanium diacene. After complete dissolution, add an organolithium salt and mechanically stir to allow the reaction to proceed; the organolithium salt is n-butyllithium. S4. After the reaction in S3 is completed, transfer the solution to the reaction chamber of an ultrasonic cavitation device under an inert gas atmosphere, add the deagglomerated silica material from S2, and perform ultrasonic cavitation treatment; the ultrasonic power of the ultrasonic cavitation treatment is 50~80kW, and the ultrasonic intensity is 30~80W / cm. 2 The ultrasonic cavitation treatment time is 2h~8h; S5. Dissolve cyclodextrin in dimethylformamide solvent to obtain cyclodextrin solution; after the reaction in S4 is completed, add the cyclodextrin solution to it for secondary treatment, so that the pre-lithiated silicon suboxide material coated with titanium cadmium enters the inner cavity of cyclodextrin. S6. After the secondary processing in S5 is completed, rotary evaporation is performed to obtain the pre-lithiated silicon-based anode material.

5. The preparation method according to claim 4, characterized in that: In step S1, the SiO particle size distribution is as follows: Dmin ≥ 3 μm, D10 ≥ 5 μm, 8 ≤ D50 ≤ 10 μm, and Dmax ≤ 14 μm.

6. The preparation method according to claim 4, characterized in that: In step S2, the protective gas is one or more of nitrogen, helium, neon, and argon. Alternatively, the carbon coating method is gas-phase carbon coating, and the carbon source gas used is one or more of methane and its homologues, ethylene and its homologues, and acetylene and its homologues; Alternatively, the volume ratio of the protective gas to the carbon source gas is 1:1 to 4:1; Alternatively, the carbon coating process is carried out at a temperature of 600℃ to 800℃ for a duration of 1 hour to 6 hours. Alternatively, the kiln rotation speed is 0.25 r / min to 2 r / min; Alternatively, the particle size of the deagglomerated material is Dmin≥3μm, D10≥5.5μm, 8.5≤D50≤10.5μm, and Dmax≤15μm.

7. The preparation method according to claim 4, characterized in that: In step S3, the inert gas is one or more of helium, neon, and argon. Alternatively, the volume ratio of the tetrahydrofuran and toluene is 1:1 to 2:1; Alternatively, the mass ratio of the titanium diacene to the organolithium salt is 1:3 to 1:6; Alternatively, the reaction time is 0.5h to 6h, and the reaction temperature is 20℃ to 60℃.

8. The preparation method according to claim 4, characterized in that: In step S4, the mass ratio of the deagglomerated silica to lithium in the organolithium salt is 9:1 to 19:1; the solid content of the deagglomerated silica is 5% to 30%. Alternatively, in step S4, the ultrasonic cavitation treatment is carried out in a cavitator equipped with a sealed reaction chamber, and the cavitator operates at a frequency of 30~1000kHz / s.

9. The preparation method according to claim 4, characterized in that: In step S5, the cyclodextrin accounts for 20% to 50% of the total mass of cyclodextrin and dimethylformamide; Alternatively, the mass ratio of the cyclodextrin to the titanium dicene added in step S3 is 1:1 to 1:2; Alternatively, the processing temperature is 120℃~200℃, and the processing time is 0.5h~4h.

10. The preparation method according to claim 4, characterized in that: In step S6, the temperature of the rotary evaporation is 150℃~250℃, and the evaporation time is 1h~3h. Alternatively, the pre-lithiated silicon-based anode material has a surface residual lithium of ≤200ppm and a pH of ≤9.

11. The application of the pre-lithiated silicon-based anode material according to any one of claims 1-3 or the pre-lithiated silicon-based anode material prepared by the method according to any one of claims 4-10 in the preparation of lithium-ion batteries.

12. A negative electrode, characterized in that: The negative electrode comprises the pre-lithiated silicon-based negative electrode material according to any one of claims 1-3 or the pre-lithiated silicon-based negative electrode material prepared by the method according to any one of claims 4-10.

13. A lithium-ion battery, characterized in that: The lithium-ion battery includes the negative electrode as described in claim 12.

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